[AD] Bug with WAV loader on latest WIP

["Chris Jones" <cj@xxxxxxxxxx>]

The latest WIP has this code in load_wav:

for (i=0; i<len*channels; i++) {
    if ((s = pack_igetw(f)) == EOF) {
       destroy_sample(spl);
       spl = NULL;
       break;
    }
    ((signed short *)spl->data)[i] = s^0x8000;
}

However, EOF is -1, which is 0xFFFF and is a valid sample for a 16-bit wave
file to have in it. Since the return value of pack_igetw is being cast to
short to be placed into s, there is no distinction between the sample 0xFFFF
and the error code -1.
This is causing load_wav to fail on some perfectly valid wave files.
I propose the following fix:

int in;
for (i=0; i<len*channels; i++) {
    if ((in = pack_igetw(f)) == EOF) {
       destroy_sample(spl);
       spl = NULL;
       break;
    }
    s = in;
    ((signed short *)spl->data)[i] = s^0x8000;
}

which reads from the file initially into a 32-bit integer, so that the
0xFFFF sample value will be accurately stored as 65535, completely distinct
from -1, the fail value.

Cheers,
Chris